TUESDAY, July 3, 2018 (HealthDay News) -- A triple whammy of genetics, smoking, and exposure to paints and solvents at work puts a person at extremely high risk of developing multiple sclerosis, Swedish researchers report.

On its own, any one factor elevates the risk for the central nervous system disease substantially, the investigators said. But when all three factors line up, the risk jumps 30-fold.

"This is a novel finding" that suggests combined risk is much higher than the sum of its parts, said study author Dr. Anna Hedstrom.

But why? Chronic lung irritation is the likely common denominator, she said, adding that ultimately it is the "immune response that results in MS, primarily in those with a genetic susceptibility to the disease."

Hedstrom works in the department of clinical neuroscience with the Institute of Environmental Medicine at the Karolinska Institute in Stockholm.

Multiple sclerosis is an often disabling disease of the central nervous system. Though the study did not prove cause and effect, and the exact cause of MS remains unclear, the U.S.-based National Multiple Sclerosis Society cites a number of possible environmental factors. Those include low vitamin D levels, childhood obesity, smoking and viral/bacterial exposure.

On the genetic front, MS experts stress that the disease is not itself an inherited illness. However, about 200 genes have been linked to MS risk.

That means that "people with a family history of MS may have a genetic susceptibility to the disease," Hedstrom said.

In fact, she noted that the gene most strongly associated with MS is quite common, carried by an estimated 30 percent of the general population.

That said, the MS society pegs the overall risk for developing MS at roughly 1 in every 750 to 1,000 people. That means that MS is rare, "and most people do not develop the disease," Hedstrom said.

In the study, Hedstrom's team collected and analyzed blood samples from just over 2,000 MS patients, alongside nearly 3,000 healthy participants.

In addition to smoking histories, all MS patients were asked to detail occupational exposure to a list of organic solvents, painting products and varnishes.

Genetic testing was done on blood samples to identify those people carrying one of two genes -- one that elevates MS risk and one that lowers it.

On average, MS patients had been 34 when first diagnosed. Those citing solvent exposure were more likely to be painters, printers and chemical engineers, said Hedstrom.

Ultimately, the researchers determined that such exposure upped MS risk by 50 percent, relative to those with no exposure.

Among those with a genetic predisposition and organic solvent exposure, MS risk rose sevenfold. About 60 percent of all the MS cases seen fell into this category.

Yet the highest MS risk by far was seen among those who also had a history of smoking. The triple threat drove up MS risk 30-fold.

The study was published July 3 online in the journal Neurology.

"More research is needed to understand the mechanisms behind our findings," said Hedstrom. "But what you can do to reduce the risk of MS, especially if you have MS in the family, is avoiding smoking and unnecessary exposure to organic solvents, and especially the combination of these exposures."

That advice was seconded by Dr. Gabriele DeLuca, an associate professor in the department of clinical neurosciences at John Radcliffe Hospital in Oxford, England. He wrote an editorial accompanying the study.

While calling for more research, DeLuca said, "in the meantime, avoidance of cigarette smoke and unnecessary exposure to organic solvents, particularly in combination, would appear reasonable lifestyle modifications to reduce the risk of MS, especially in those with a family history of the disease."